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Window to
the past

How long has Central America
been so biologically diverse?

September 28, 2017

20-million-year-old fossil seeds shed light on origins of plant biodiversity in Panama.

While exploring the little-studied rock formations of Panama’s Azuero Peninsula last June, a group of geology undergrads from Colombia’s Universidad de los Andes happened upon a tiny creek that trickles through farmers’ fields before emptying into Río Palo Seco en route to the Pacific. With a few swings of their rock hammer, they unearthed dozens of almond-sized fossilized seeds that opened a new window into Panama’s tropical climate 20 million years ago.

The Neotropical rainforest is the ecosystem with the greatest number of plant species on Earth but it is a mystery when this ecosystem was established in Central America.

The seeds belong to a South American plant family called Humiriaceae — large trees found in humid, lowland forests. Their presence may indicate that Azuero’s hot, dry climate — which has no trees from that family today — was much different when the first landscapes of Panama were forming and not connected to South America. The fossils suggest currents from the southern continent delivered the seeds, and the sediments that contain the fossils show a lowland river system existed in the area at the time.

Nicolás Pérez, a short-term STRI fellow and undergrad at the university, collected and analyzed more seeds this year. He finely sliced them with an electric saw in STRI’s paleontology lab, viewed the samples under high-powered microscopes and described their well-preserved inner structure, tissues and cells. Pérez hopes to explain when lower Central America, which is much younger than the continents it connects, became a hotspot for plant biodiversity. “Is it something new or something that has been around for a long time?” he asks.

“The Neotropical rainforest biome is the ecosystem with the greatest number of plant species on the planet but it is a mystery when this ecosystem was established in Central America,” says Pérez. “Understanding the origin and evolution of the Neotropical forest in a paleobiological context is crucial to understand its future. By combining fossil and paleoclimatic data we get a better idea of how these forests will react to climate change.”

So far, the seeds are the only species the university’s students have found in Panama’s Torio area but he hopes future fieldwork will turn up more. “There are many rocks left to discover and fossils to find and study,” he said.

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